Download Vector-Borne Diseases: Trypanosomiasis

Vector-Borne Diseases:
Trypanosomiasis
April 1st, 2010
The Pathogen
• Genus Trypanosoma
• Two species of human health importance:
– Trypanosoma brucei
– Trypanosoma cruzi
• The T. brucei complex (2 subspecies):
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Trypanosoma brucei rhodesiense
Trypanosoma brucei gambiense
Cannot tell them apart by morphology
Cause distinct disease entities
The Pathogen
• Protozoan hemoflagellates
– Single celled
– flagella
• Complex life cycle
– Vector
– Human
– animals
• Reservoirs:
– Humans
– Cattle
The Pathogen
Trypanosoma brucei ssp. in thin blood smears stained
with Giemsa.
Overview
• Three types of trypanosomiasis
– West African (sleeping sickness)
– East African (sleeping sickness)
– American (Chaga’s disease)
• Differences
– Geographic distribution
– Vectors
– Disease process
West African Trypanosomiasis
• Sleeping sickness
• Trypanosoma brucei gambiense
• Geographic distribution
– Western and Central Africa
– Vector distribution
• Always fatal without treatment
• Disease course over years
– acute and chronic phases
West African Trypanosomiasis
• This form is ~95% of reported cases
• 12,000-15,000 reported cases/year, WHO
estimates 50-60,000 are really infected
• Humans are the reservoir
• Disease of rural areas; urban transmission
is rare
East African Trypanosomes
• Trypanosoma brucei rhodesiense
• Geographic distribution
– East and Southeast Africa
• Always fatal without treatment
• Acute course compared to gambiense form
• Cattle are additional reservoir
Cases of African trypanosomiasis
Geographic distribution
Geographic distribution
The vector
• Tsetse fly
• Glossina species
• Takes a blood meal
• trypomastigotes are the form transmitted
to the host
• Daytime feeder
• Savannah and riverine flies
Life Cycle: Trypanosomes
Disease
• Length of disease process differs between two
• Sore may develop at site of initial inoculation
– hemolymphatic stage
– fever, lymphadenopathy, and pruritus.
• meningoencephalitic stage
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Parasite crosses blood-brain barrier
invasion of the central nervous system
headaches, somnolence, abnormal behavior
loss of consciousness and coma
• more acute disease with T. b. rhodesiense than T.
b. gambiense.
Immunity
• Humans do mount immune response
• No residual immunity
• cyclic fluctuation in the number of
parasites in blood
• Each new wave of parasite represents a
different antigenic variant
Diagnosis
• Microscopic examination
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chancre fluid
lymph node aspirates
Blood
bone marrow
cerebrospinal fluid (late stages of infection)
• smear stained with Giemsa
Treatment
• Pentamidine isethionate
– hemolymphatic stage of West African
• suramin
– hemolymphatic stage of East African
• Melarsoprol
– arsenical
– late disease with central nervous system involvement
– T.b. gambiense or T. b. rhodiense
• Eflornithine
– Expensive
– not widely available
– effective only for West African
Control
• Bite prevention
– Difficult with daytime biters
• Control vector habitats
• Treat infected people
– Screening methods are available
• Bednets not useful
Vector control
• Control with insecticides
– sequential aerosol spraying technique (SAT)
– ground spraying
– insecticide-treated targets or insecticidetreated animals
• Traps
• sterile insect technique (SIT).
American trypanosomiasis
• Chaga’s Disease
• Trypanosoma cruzi
• Geographic distribution
– southern United States to southern Argentina
• A disease of poor, rural areas of Mexico,
Central America, and South America
• Humans and animals are reservoir
Geographic distribution
Vector
• triatomine bugs (kissing bugs)
• Triatoma, Rhodinius, and Panstrongylus
• Takes a blood meal
• Releases trypomastigotes in its feces near
the site of the bite
• Enter host through the wound
Life Cycle: Chaga’s disease
Disease
• Acute phase
– usually asymptomatic
– fever, anorexia, lymphadenopathy, myocarditis
– Lesion (chagoma) at site of inoculation
• Resolve over a period of a few weeks or months
into an asymptomatic chronic form
– 20-30% of cases
• Years or decades after initial infection:
– cardiomyopathy
– GI complications
– can be fatal
Diagnosis
• Microscopic examination
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fresh anticoagulated blood
thin and thick blood smears stained with
Giemsa
• Isolation of the agent:
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inoculation in culture with specialized
media
inoculation into mice
xenodiagnosis
Treatment
• Benznidazole
• nifurtimox
• Treatment is most effective during the
acute phase
• Drugs are fairly toxic
• IND protocol from the CDC
Control
• Vector control
• Poorly constructed houses and houses
with thatched roofs are at risk
• Treatment of houses with insecticides
• Get rid of places in dwellings where
vector and reservoir animals can live and
breed
• Bednets